The process of call note learning in two populations of a finch, the pine grosbeak, with different call characteristics will be investigated. The experiment will be to breed the two populations of grosbeaks in acoustically isolated aviaries, exchanging the fresh eggs between pairs from the different populations, and recording the process of call development in the cross-fostered juveniles. The experiment is of relevance to basic learning theory, because some pine grosbeak relatives are reported to have calls alterable by learning in both non-breeding social and breeding situations, and because preliminary results have shown that there may be an interplay of genetic and environmental factors in the development of the calls in pine grosbeaks.